Optical glass, glass preform, optical element and optical instrument having the same

ABSTRACT

Disclosed are an optical glass, a glass preform, an optical element and an optical instrument having the same. The optical glass comprises 5 to 25 wt % of B2O3, 25 to 45 wt % of La2O3, 0 to 10 Wt % of Y2O3, 10 to 35 wt % of Gd2O3, 0.5 to 15 wt % of SiO2, 1 to 15 wt % of ZrO2, 0 to 5 wt % of TiO2, 0 to 7 wt % of WO3, 0 to 15 wt % of Ta2O5, 0 to 10 wt % of ZnO and 0 to 8.5 wt % of Nb2O5; and m(B2O3+SiO2+ZrO2+Nb2O5+TiO2+WO3)/m(La2O3+ZrO2) is not lower than 0.6.

TECHNICAL FIELD

The present disclosure belongs to the field of optical glass, in particular the present disclosure relates to an optical glass, a glass preform, an optical element and an optical instrument having the same.

BACKGROUND

High-refractivity and low-dispersion optical glass can simplify optical systems, eliminate spherical aberration, chromatic aberration and image quality distortion, and expand visual field of lens, is significant to improve imaging quality of optical instruments, and enables lens to realize miniaturization and light weight, thus better meeting the requirements of novel optoelectronic products for high imaging quality. Especially, there is a great market demand for the high-refractivity and low-dispersion optical glass with refractive index (nd) greater than 1.86 and Abbe number (vd) greater than 38.8.

In general, a great amount of rare earth oxides are introduced to formula systems of the high-refractivity and low-dispersion glass to improve refractive index of glass. However, in different formula systems, excessive lanthanide oxides will affect glass forming ability, bringing difficulty to manufacturing by mass production process. Therefore, the optical glass composition of the prior art needs to be further explored.

DISCLOSURE

The present disclosure aims to solve one of the technical problems in the prior art to a certain extent. To this end, an object of the present disclosure is to propose an optical glass, a glass preform, an optical element and an optical instrument having the same, and the optical glass has a refractive index (nd) greater than 1.86 and an Abbe number (vd) greater than 38.8, thus solving such technical problems of high-refractivity and low-dispersion optical glass as easy devitrification, great difficulty in mass production and high cost in the prior art.

In one aspect of the present disclosure, the present disclosure proposes an optical glass. According to embodiments of the present disclosure, the optical glass comprises 5 to 25 wt % of B₂O₃, 25 to 45 wt % of La₂O₃, 0 to 10 wt % of Y₂O₃, 10 to 35 wt % of Gd₂O₃, 0.5 to 15 wt % of SiO₂, 1 to 15 wt % of ZrO₂, 0 to 5 wt % of TiO₂, 0 to 7 wt % of WO₃, 0 to 15 wt % of Ta₂O₅, 0 to 10 wt % of ZnO and 0 to 8.5 wt % of Nb₂O₅, wherein m_((B2O3+SiO2+ZrO2+Nb2O5+TiO2+WO3))/m_((La2O3+ZrO2)) is not lower than 0.6.

The inventors find that by controlling components, contents and use ratio between specific components, the optical glass of the present disclosure is capable of resulting in high-refractivity and low-dispersion optical glass with devitrification resistance and excellent properties (optical glass with refractive index (nd) greater than 1.86, and Abbe number (vd) greater than 38.8) by using a little or no Ta₂O₅, and the optical glass of the present disclosure has low production cost and high availability for mass production.

In addition, the optical glass according to the embodiment of the present disclosure can also have the following additional technical features:

In some embodiments of the present disclosure, the optical glass comprises 8 to 20 wt % of B₂O₃, and/or 30 to 42 wt % of La₂O₃, and/or 0 to 8 wt % of Y₂O₃, and/or 15 to 28 wt % of Gd₂O₃, and/or 2 to 13 wt % of SiO₂, and/or 1 to 10 wt % of ZrO₂, and/or 0.1 to 5 wt % of TiO₂, and/or 0.1 to 5 Wt % of WO₃, and/or 0.5 to 10 wt % of Ta₂O₅, and/or 0 to 5 wt % of ZnO, and/or 0 to 8.5 wt % of Nb₂O₅. Hence, the optical glass can be ensured to have excellent properties.

In some embodiments of the present disclosure, the optical glass comprises 10 to 16 wt % of B₂O₃, and/or 33 to 39 wt % of La₂O₃, and/or 1 to 5 wt % of Y₂O₃, and/or 17 to 25 wt % of Gd₂O₃, and/or 4 to 10 wt % of SiO₂, and/or 3 to 8 wt % of ZrO₂, and/or 0.5 to 3 wt % of TiO₂, and/or 0.5 to 4 Wt % of WO₃, and/or 3 to 10 wt % of Ta₂O₅, and/or 1 to 3 wt % of ZnO, and/or 0 to 8.5 wt % of Nb₂O₅. Hence, the optical glass can be ensured to have excellent properties.

In some embodiments of the present disclosure, in the optical glass composition, m_((B2O3+SiO2+ZrO2+Nb2O5+TiO2+WO3))/m_((La2O3+ZrO2)) is not lower than 0.65, preferably 0.65 to 0.72. Hence, the optical glass can be further ensured to have excellent properties.

In some embodiments of the present disclosure, in the optical glass composition, m_((ZrO2+TiO2+La2O3))/m_((Nb2O5+SiO2+WO3+Gd2O3)) is equal b 1.0 to 1.6, preferably 1.1 to 1.45, and more preferably 1.35 to 1.42. Hence, the optical glass can be further ensured to have excellent properties.

In some embodiments of the present disclosure, the optical glass further comprises 0 to 1 wt % of Sb₂O₃, and/or 0 to 1 wt % of SnO₂, and/or 0 to 1 wt % of CeO₂, and/or 0 to 10 wt % of Yb₂O₃, and/or 0 to 10 wt % of Lu₂O₃, and/or 0 to 10 wt % of Al₂O₃, and/or 0 to 10 wt % of Bi₂O₃, and/or 0 to 10 wt % of GeO₂, and/or 0 to 10 wt % of total amount of Li₂O, Na₂O and K₂O, and/or 0 to 10 wt % of total amount of CaO, SrO, BaO and MgO. Hence, the optical glass can be further ensured to have excellent properties.

In some embodiments of the present disclosure, refractive index of the optical glass is greater than 1.86, preferably 1.87 to 1.89, and Abbe number thereof is greater than 38.8, preferably 39.0 to 41.0.

In some embodiments of the present disclosure, λ₇₀ of the optical glass is not greater than 420 nm, preferably not greater than 390 nm, and λ₅ thereof is not greater than 360 nm, preferably not greater than 350 nm.

In some embodiments of the present disclosure, an upper limit of devitrification temperature of the optical glass is not higher than 1350° C., preferably not higher than 1300° C.

In some embodiments of the present disclosure, durability of water of the optical glass is not lower than grade 3, preferably not lower than grade 2; durability of acid thereof is not lower than grade 3, preferably not lower than grade 2; and climatic resistance thereof is not lower than grade 3, preferably not lower than grade 2.

In some embodiments of the present disclosure, striae of the optical glass are above grade C, preferably above grade B, and more preferably above grade A.

In some embodiments of the present disclosure, extent of bubble of the optical glass is not lower than grade A, preferably not lower than grade A₀, and more preferably grade A₀₀.

In some embodiments of the present disclosure, density of the optical glass is not higher than 5.6 g/cm³, preferably not higher than 5.5 g/cm³.

In the second aspect of the present disclosure, the present disclosure proposes a glass preform. According to embodiments of the present disclosure, the glass preform is made of the optical glass. Hence, the glass preform made of the high-refractivity and high-dispersion optical glass has excellent properties, thus meeting the market demand.

In the third aspect of the present disclosure, the present disclosure proposes an optical element. According to embodiments of the present disclosure, the optical element is made of the optical glass or the glass preform. Hence, the optical element made of the high-refractivity and high-dispersion optical glass or the glass preform has excellent properties, thus meeting the market demand.

In the fourth aspect of the present disclosure, the present disclosure proposes an optical instrument. According to embodiments of the present disclosure, the optical instrument has the optical element. Hence, customer experience of the optical instrument can be improved by using the optical element with the excellent properties thereon.

Additional aspects and advantages of the present disclosure will be set forth in part in the description below and, in part, will become obvious from the description below, or can be learned by practice of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described in detail below. The embodiments described below are exemplary and aim to explain the present disclosure, and cannot be construed as limitations thereto.

In one aspect of the present disclosure, the present disclosure proposes an optical glass. According to embodiments of the present disclosure, the optical glass comprises 5 to 25 wt % of B₂O₃, 25 to 45 wt % of La₂O₃, 0 to 10 wt % of Y₂O₃, 10 to 35 wt % of Gd₂O₃, 0.5 to 15 wt % of SiO₂, 1 to 15 wt % of ZrO₂, 0 to 5 wt % of TiO₂, 0 to 7 wt % of WO₃, 0 to 15 wt % of Ta₂O₅, 0 to 10 wt % of ZnO and 0 to 8.5 wt % of Nb₂O₅, wherein m_((B2O3+SiO2+ZrO2+Nb2O5+TiO2+WO3))/m_((La2O3+ZrO2)) is not lower than 0.6.

Glass Composition:

B₂O₃ is a component to form skeleton of glass, and has functions of improving meltability and devitrification resistance and reducing dispersion of glass in the present disclosure. When introduced amount of B₂O₃ is more than 25 wt %, stability and refractive index of glass decrease; and when the introduced amount thereof is less than 5 wt %, the meltability of glass decreases, which cannot reach the optical constant required by the present disclosure. Therefore, in the present disclosure, B₂O₃ content is 5 to 25 wt %, preferably 8 to 20 wt %, and more preferably 10 to 16 wt %.

La₂O₃ is an indispensable component to obtain the optical properties required by the present disclosure. When La₂O₃ content is less than 25 wt %, it is difficult to realize the required optical properties, but when the content thereof is more than 45 wt %, the devitrification resistance and meltability of glass deteriorate. Therefore, in the present disclosure, the La₂O₃ content is 25 to 45 wt %, preferably 30 to 42 wt %, and more preferably 33 to 39 wt %.

Y₂O₃ can improve the meltability, devitrification resistance of glass and reduce upper limit of devitrification temperature of glass, but when content thereof is more than 10 wt %, the stability and devitrification resistance of glass decrease. Therefore, in the present disclosure, the Y₂O₃ content is 0 to 10 wt %, preferably 0 to 8 wt %, and more preferably 1 to 5 wt %.

In the present disclosure, Gd₂O₃ and La₂O₃ coexist, which can improve the stability of the formed glass. However, when Gd₂O₃ content is lower than 10 wt %, the effect is not obvious; and when the content thereof is more than 35 wt %, the devitrification resistance of glass decreases, and the stability of the formed glass deteriorates. Therefore, in the present disclosure, the Gd₂O₃ content is 10 to 35 wt %, preferably 15 to 28 wt %, and more preferably 17 to 25 wt %.

SiO₂ is a component to form skeleton of glass, and has functions of improving the devitrification resistance, climatic resistance and thermal stability of glass. However, when SiO₂ content is lower than 0.5 wt %, the function of improving the devitrification resistance is not obvious; and when the content thereof is more than 15 wt %, the meltability of glass decreases, and the refractive index required by the disclosure is not available. Therefore, in the present disclosure, the SiO₂ content is 0.5 to 15 wt %, preferably 2 to 13 wt %, and more preferably 4 to 10 wt %.

ZrO₂ is a component to improve the refractive index and stability, and has functions of improving the devitrification resistance and chemical durability due to the fact of forming glass as an intermediate oxide. When ZrO₂ content is less than 1 wt %, the intended effect is not available, and when the ZrO₂ content is more than 15 wt %, there is a tendency that devitrification tendency becomes strong and vitrification becomes difficult. Therefore, in the present disclosure, the ZrO₂ content is 1 to 15 wt %, preferably 1 to 10 wt %, and more preferably 3 to 8 wt %.

TiO₂ also has a function of increasing the refractive index of glass, and can involve formation of glass network, and appropriate introduction thereof can make glass stabler. However, when TiO₂ content is more than 5 wt %, dispersion of glass increases significantly, transmittance of short waves in the visible region of glass decreases, and tendency of coloring of glass increases. Therefore, in the present disclosure, the TiO₂ content is 0 to 5 wt %, preferably 0.1 to 5 wt %, and more preferably 0.5 to 3 wt %.

WO₃ plays the role of improving the refractive index. However, when the content thereof is more than 7 wt %, the dispersion increases significantly, the transmittance on the long side of short waves in the visible region of glass decreases, and the tendency of coloring of glass increases. Therefore, in the present disclosure, the WO₃ content is 0 to 7 wt %, preferably 0.1 to 5 wt %, and more preferably 0.5 to 4 wt %.

Ta₂O₅ has functions of improving the refractive index and maintaining low dispersion of glass. However, due to higher price than other components, when the content thereof is more than 15 wt %, cost of the optical glass increases. Therefore, usage of Ta₂O₅ is decreased in the perspective of utility and cost. In the present disclosure, the Ta₂O₅ content is 0 to 15 wt %, preferably 0.5 to 10 wt %, and more preferably 3 to 10 wt %.

ZnO can adjust the refractive index and dispersion of glass, and a proper amount of ZnO can play a role of improving the stability or meltability of glass and enhancing compressive formability. However, when ZnO content is more than 10 wt %, the refractive index decreases, failing to meet requirements of the present disclosure; and the devitrification resistance of glass decreases, and the upper limit of devitrification temperature rises. Therefore, in the present disclosure, the ZnO content is 0 to 10 wt %, preferably 0 to 5 wt %, and more preferably 1 to 3 wt %.

Nb₂O₅ is a high-refractivity and high-dispersion component and capable of increasing the refractive index without significantly increasing dispersion, and also has functions of improving anti-devitrification and chemical stability of glass. However, when Nb₂O₅ content is more than 8.5 wt %, the optical properties of the glass of the present disclosure cannot be obtained, and the devitrification resistance of glass deteriorates. Therefore, in the present disclosure, the Nb₂O₅ content is 0 to 8.5 wt %, preferably 0.

The inventors find that the optical glass of the present application requires excellent optical properties, devitrification resistance, chemical stability, climatic resistance, bubble grade and striae grade as well as low upper limit of devitrification temperature. Through a lot of researches, the inventors of the present application find that by controlling ratio of total weight of B₂O₃, SiO₂, ZrO₂, Nb₂O₅, TiO₂ and WO₃ in the glass composition to total weight of La₂O₃ and ZrO₂ to be not lower than 0.6 and making the components play a synergistic role, gas solubility can be effectively controlled during glass melting, the resulting glass is reluctant to devitrify, optical constant of the glass improves, the chemical stability and uniformity improve, so that the optical glass has the refractive index greater than 1.86, the Abbe number greater than 38.8, the upper limit of devitrification temperature not higher than 1350° C., the durability of water not lower than grade 3, the durability of acid not lower than grade 3, the climatic resistance not lower than grade 3, the striae above grade C, and the extent of bubble not lower than grade A, and the resulting optical glass has excellent devitrification resistance; and by further preferably controlling the ratio of the total weight of B₂O₃, SiO₂, ZrO₂, Nb₂O₅, TiO₂ and WO₃ to the total weight of La₂O₃ and ZrO₂ to be not lower than 0.65, more preferably 0.65 to 0.72, the resulting optical glass has the refractive index of 1.87 to 1.89, the Abbe number of 39.0 to 41.0, the upper limit of devitrification temperature not higher than 1300° C., the durability of water not lower than grade 2, the durability of acid not lower than grade 2, the climatic resistance not lower than grade 2, the striae above grade B, more preferably not lower than grade A, and the extent of bubble not lower than grade A₀, more preferably grade A₀₀.

The inventors also find that the optical glass of the present application further requires excellent transmittance and light-weight property. Through a lot of researches, the inventors of the present application find that by controlling ratio of total weight of ZrO₂, TiO₂ and La₂O₃ to total weight of Nb₂O₅, SiO₂, WO₃ and Gd₂O₃ to be 1.0 to 1.6, the gas solubility can be effectively controlled during melting, the transmittance and chemical stability of glass improve, light weight is realized, and the resulting optical glass has λ₇₀ not more than 420 nm, λ₅ not more than 360 nm, density not higher than 5.6 g/cm³, the durability of water not lower than grade 3, the durability of acid not lower than grade 3, and the extent of bubble not lower than grade A; and by further preferably controlling the ratio of the total weight of ZrO₂, TiO₂ and La₂O₃ to the total weight of Nb₂O₅, SiO₂, WO₃ and Gd₂O₃ to be 1.1 to 1.45, more preferably 1.35 to 1.42, the resulting optical glass has λ₇₀ not more than 390 nm, λ₅ not more than 350 nm, the density not higher than 5.5 g/cm³, the durability of water not lower than grade 2, the durability of acid not lower than grade 2, and the extent of bubble not lower than grade A₀, more preferably grade A₀₀.

According to a further embodiment of the present disclosure, the optical glass further comprises 0 to 1 wt % of Sb₂O₃, and/or 0 to 1 wt % of SnO₂, and/or 0 to 1 wt % of CeO₂, and/or 0 to 10 wt % of Yb₂O₃, and/or 0 to 10 wt % of Lu₂O₃, and/or 0 to 10 wt % of Al₂O₃, and/or 0 to 10 wt % of Bi₂O₃, and/or 0 to 10 wt % of GeO₂, and/or 0 to 10 wt % of total amount of Li₂O, Na₂O and K₂O and/or 0 to 10 wt % of total amount of CaO, SrO, BaO and MgO. The inventors find that addition of a small amount of Sb₂O₃ and/or SnO₂ and/or CeO₂ can improve clarification effect of glass, but when Sb₂O₃ content is more than 1 wt %, the glass has a tendency of clarification performance decrease, and strong oxidation action thereof promotes forming molds to deteriorate. Therefore, in the present disclosure, addition amount of Sb₂O₃ is preferably 0 to 1 wt %, more preferably 0 to 0.5 wt %, and further preferably 0. SnO₂ also can be added as a clarificant, but when content thereof is more than 1 wt %, the coloring of glass occurs, or when glass is subject to heating, softening and compression molding for secondary forming, Sn will become starting point of nucleation, generating a tendency of devitrification. Therefore, in the present disclosure, the SnO₂ content is preferably 0 to 1 wt %, more preferably 0 to 0.5 wt %, and further preferably 0. CeO₂ has the same function and addition proportion as SnO₂, and content thereof is preferably 0 to 1 wt %, more preferably 0 to 0.5 wt %, and further preferably 0. Yb₂O₃ is also a component having high refractive index and low dispersion in the glass of the present disclosure, when content thereof is more than 10 wt %, the stability and devitrification resistance of the glass decreases, therefore Yb₂O₃ content is preferably 0 to 10 wt %, more preferably 0 to 8 wt %, and further preferably 0. Lu₂O₃ can improve the refractive index and decrease the dispersion of glass, but when content thereof is more than 10 wt %, the devitrification resistance and meltability of glass deteriorate, and higher price thereof than other components result in increase in cost of the optical glass. Therefore, in the present disclosure, the Lu₂O₃ content is 0 to 10%, preferably 0 to 8 wt %, and more preferably 0. Introduction of a small amount of Al₂O₃ can improve the stability and chemical stability of the formed glass, but when the content thereof is more than 10 wt %, there is a tendency that the meltability of glass deteriorates and the devitrification resistance decreases. Therefore, in the present disclosure, the Al₂O₃ content is preferably 0 to 10 wt %, and more preferably 0 to 8 wt %. Bi₂O₃ can increase the refractive index of glass, but excessive addition thereof can lower transmittance on the long side of short waves in the visible region and shows a tendency of coloring of glass. Therefore, in the present disclosure, the Bi₂O₃ content is preferably 0 to 10 wt %, more preferably 0 to 5 wt %, and further preferably 0. GeO₂ also can effectively improve the stability and devitrification resistance of the formed glass. However, GeO₂ is very expensive, therefore, the GeO₂ content is preferably 0 to 10 wt %, more preferably 0 to 5 wt %, and further preferably 0. Li₂O, Na₂O and K₂O are components to inhibit phase splitting and improve the stability of glass. When the total content thereof is more than 10 wt %, there is a tendency of significantly decreasing the climatic resistance or decreasing the refractive index. Therefore, in the present disclosure, the total weight of Li₂O, Na₂O and K₂O is 0 to 10 wt %, more preferably 0 to 5 wt %, and further preferably 0. Such alkali-earth oxides as CaO, SrO, BaO and MgO can decrease the climatic resistance and significantly increase the upper limit of devitrification temperature of glass. However, when total content thereof is more than 10 wt %, the devitrification resistance of glass decreases. Therefore, in the present disclosure, the total weight of CaO, SrO, BaO and MgO is preferably 0 to 10 wt %, more preferably 0 to 5 wt %, and further preferably 0.

Properties and test methods of the optical glass of the present disclosure are described below.

1. Color code (λ₇₀/λ₅) Short wave transmission spectral characteristic of the glass of the present disclosure is expressed as Color code (λ₇₀/λ₅). λ₇₀ is the corresponding wavelength when the glass transmittance reaches 70%, λ₅ is the corresponding wavelength when the glass transmittance reaches 5%, and λ₇₀ is determined by measuring the wavelength with spectral transmittance in the wavelength domain from 280 nm to 700 nm and transmittance reaching 70% using two pieces of mutually parallel glass with thickness of optically polished relative planes being 10±0.1 mm. The spectral transmittance or transmittance is an amount indicated by I_(out)/I_(in) in the case where light with intensity I_(in) is incident perpendicularly to the surfaces of the glass, passes through the glass and emits light with intensity I_(out) from a plane, and includes the transmittance of the surface reflection lost on the surfaces of the glass. The higher the refractive index of glass, the greater the surface reflection loss. Therefore, for the glass with high refractive index, low value of λ₇₀ means less self-coloring of glass. When the transmittance of the optical glass of the present disclosure reaches 70%, the corresponding wavelength (λ₇₀) is not more than 420 nm, preferably not more than 390 nm; and when the transmittance thereof reaches 5%, the corresponding wavelength (λ₅) is not more than 360 nm, preferably not more than 350 nm.

The spectral transmittance is measured by using a glass sample having a thickness of 10±0.1 mm with two opposing optically polished planes, and calculated on the basis of the result.

2. Density

Density of optical glass is the weight of unit volume at 20° C., and expressed in g/cm³. The optical glass of the present disclosure has a density not higher than 5.6 g/cm³, preferably not higher than 5.5 g/cm³.

The density is measured according to the method specified in GB/T7962.20-2010.

3. Upper Limit of Devitrification Temperature The devitrification property of glass is measured by gradient furnace method which comprises the following steps: processing the glass into 180*10*10 mm samples, polishing sides, placing the samples into a furnace with temperature gradient (5° C./cm), raising temperature to 1400° C., taking out the samples after holding for 4 hours, naturally cooling to room temperature, and observing devitrification of the glass under a microscope, and the maximum temperature corresponding to appearance of crystals is the upper limit of devitrification temperature of glass. The lower the upper limit of devitrification temperature of glass, the stronger the stability of glass at high temperature, and the better the production process performance. According to a typical embodiment of the present disclosure, preferably, the upper limit of devitrification temperature of the optical glass is not higher than 1350° C., preferably not higher than 1300° C., and more preferably not higher than 1280° C.

4. Chemical Stability (Durability of Water (D_(W)) and Durability of Acid (D_(A))

During manufacturing and use of optical glass elements, the ability of the polished surface of optical glass to resist action of erosive media such as water and acid is called chemical stability of optical glass, and the ability mainly depends on chemical composition of glass. The durability of water (D_(W)) (powder method) of the optical glass of the present disclosure is not lower than grade 3, preferably not lower than grade 2, and more preferably not lower than grade 1; and the durability of acid (D_(A)) thereof (powder method) is not lower than grade 3, preferably not lower than grade 2, and more preferably not lower than grade 1.

The durability of water (D_(W)) and the durability of acid (D_(A)) are tested according to the methods specified in GB/T 17129.

5. Bubble

The extent of bubble refers to grade of allowable bubble content of glass. Bubble affects appearance quality of glass products as well as optical properties, transparency and mechanical strength of optical glass, and causes a lot of adverse effects. Therefore, it is crucial to control the extent of bubble of glass. The optical glass of the present disclosure has the extent of bubble not lower than grade A, preferably not lower than grade A₀, and more preferably grade A₀₀.

The bubble quality of the optical glass is measured according to the method specified in GB/T7962.8-2010.

6. Refractive Index and Abbe Number

The optical glass of the present disclosure has high refractive index and low dispersion, and a lens made of the glass with high refractive index and low dispersion is generally combined with a lens made of glass with high refractive index and high dispersion to correct chromatic aberration. In addition, in the case that the optical glass is used as a lens, the higher the refractive index, the thinner the lens, which is conducive to miniaturization of optical equipment. For the optical glass of the present disclosure, the refractive index (nd) is more than 1.86, preferably nd is 1.87 to 1.89; and the Abbe number (vd) is more than 38.8, preferably vd is 39.0 to 41.0.

The refractive index and the Abbe number are measured according to the method specified in GB/T7962.1-2010.

7. Striae

For degree of striae, with a striae meter composed of a point light source and a lens, striae are viewed in the direction of maximum visibility, and compared with a standard sample. The striae are classified into 4 grades namely grade A, grade B, grade C and grade D. Grade A striae are invisible to the naked eye under specified testing conditions, grade B striae are fine and scattered striae under specified testing conditions, grade C striae are slight parallel striae under specified testing conditions, and grade D striae are rough striae under specified testing conditions. The striae of the optical glass of the present disclosure are above grade C, preferably above grade B, and more preferably grade A.

Striae are measured according to the method specified in MLL-G-174B.

8. Climatic resistance

Testing samples are placed in a testing box exposed to saturated water vapor atmosphere with relative humidity of 90%, temperature of the testing box alternates between 40° C. and 50° C. per hour, and the periodic change lasts for 15 times. Climatic resistance is categorized based on change in haze before and after testing, and haze refers to such degeneration layers as “fish eye” and “blushing” on the surface of colorless optical glass generated by atmospheric erosion. The degree of erosion on glass surface is determined by measuring difference in haze before and after erosion of the samples. The haze is measured by a turbidimeter with integrating sphere having relative deviation of haze indication within ±5%. The table below shows classification of climatic resistance:

4 Category 1 2 3 a b c Increase in <0.3 0.3-1.0 1.0-2.0 2.0-4.0 4.0-6.0 ≥6.0 haze, ΔH(%)

The climatic resistance of the glass of the present disclosure is not lower than grade 3, preferably not lower than grade 2, and more preferably not lower than grade 1.

In the second aspect of the present disclosure, the present disclosure proposes a glass preform. According to embodiments of the present disclosure, the glass preform is made of the optical glass. Hence, the glass preform of the present disclosure has properties of high refractive index and low dispersion, thus meeting the market demand for high-performance glass. Specifically, the resulting optical glass is cut into predetermined size, uniformly coated with a release agent composed of boron nitride powder on the surface thereof, and heated, softened, and compression molded to make preforms for such lenses and prisms as concave meniscus lens, convex meniscus lens, biconvex lens, biconcave lens, plano-convex lens and plano-concave lens. It should be noted that the features and advantages described for theoptical glass also apply to the glass preform, and are not repeated here.

In the third aspect of the present disclosure, the present disclosure proposes an optical element. According to embodiments of the present disclosure, the optical element is made of the optical glass or the glass preform. Hence, the optical element of the present disclosure has properties of high refractive index and low dispersion, and can be made into such optical instruments as lenses and prisms with excellent properties at low cost. For example, when the optical element is used as a lens, the optical element can be used as convex meniscus lens, concave meniscus lens, biconvex lens, biconcave lens, plano-convex lens or plano-concave lens with lens face being spherical surface or aspheric surface. Such lens is combined with a lens made of glass with high refractive index and high dispersion to correct the chromatic aberration, and suitable for being as a lens for correcting chromatic aberration. In addition, such lens is also conducive to making compact optical systems. In addition, for prism, due to the high refractive index, a compact wide-angle optical system can be realized by combining the prism into an optical system and directing to the desired direction via a curved optical path. Specifically, the glass preform is annealed, and trimmed while reducing internal deformation of the glass so that optical properties such as the refractive index reach desired values, and then the preforms are milled and ground to make such lenses and prisms (i.e. optical elements) as concave meniscus lens, convex meniscus lens, biconvex lens, biconcave lens, plano-convex lens and plano-concave lens, and surfaces of the resulting optical elements can be coated with an anti-reflection film. It should be noted that the features and advantages described for the optical glass and the glass preform also apply to the optical element, and are not repeated here.

In the fourth aspect of the present disclosure, the present disclosure proposes an optical instrument. According to embodiments of the present disclosure, the optical instrument has the optical element. Hence, customer experience of the optical instrument can be improved by using the optical element with the excellent properties thereon. Specifically, the optical instrument of the present disclosure can be a digital camera or video camera. It should be noted that the features and advantages described for the optical element also apply to the optical instrument, and are not repeated here.

The present disclosure is described with reference to embodiments. It should be noted that the embodiments are descriptive only and do not limit the present disclosure in any way.

In order to obtain the glass with components shown in Table 1 to Table 5, carbonate, nitrate, hydroxides, oxides and boric acid are used as raw materials, the raw materials corresponding to the components of the optical glass are weighed proportionally and thoroughly mixed to obtain a blended raw material which is placed into a platinum crucible, heated to 1200 to 1450° C., melted, agitated and clarified to form uniform molten glass, and the molten glass is moderately cooled and poured into a preheated mold, kept at 650 to 700° C. for 2 to 4 hours and slowly cooled to obtain the optical glass. In addition, the properties of the glass are measured according to the above methods, and the measurement results are shown in Table 1 to Table 5.

TABLE 1 Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Component (wt %) ment 1 ment 2 ment 3 ment 4 ment 5 ment 6 ment 7 ment 8 ment 9 B₂O₃ 10.0 13.0 11.0 10.4 15.0 11.0 13.0 10.8 10.3 La₂O₃ 39.0 34.0 34.0 34.8 35.0 36.5 37.0 35.8 36.2 Y₂O₃ 0.0 5.0 5.0 4.6 5.0 3.2 2.5 5.0 4.5 Gd₂O₃ 14.0 23.0 21.0 23.0 20.0 23.0 22.0 22.8 19.0 SiO₂ 13.0 5.0 5.0 7.0 4.0 5.0 8.0 7.6 8.0 ZrO₂ 8.0 4.1 5.0 7.0 7.6 5.0 4.0 6.0 6.3 TiO₂ 0.1 1.9 3.0 3.0 0.0 3.0 1.0 2.7 1.0 WO₃ 7.0 1.0 4.0 2.2 5.0 4.0 1.0 1.0 4.0 Ta₂O₅ 1.8 10.0 9.0 7.0 0.5 7.0 8.5 7.3 7.8 ZnO 0.0 3.0 3.0 1.0 2.4 2.3 3.0 1.0 2.9 Nb₂O₅ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Sb₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SnO₂ 1.0 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 CeO₂ 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Yb₂O₃ 3.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lu₂O₃ 2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Al₂O₃ 0.0 0.0 0.0 0.0 2.0 0.0 0.0 0.0 0.0 Bi₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 GeO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Li₂O + Na₂O + K₂O 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CaO + SrO + BaO + MgO 0.0 0.0 0.0 0.0 3.0 0.0 0.0 0.0 0.0 (B₂O₃ + SiO₂ + 0.81 0.66 0.72 0.71 0.74 0.67 0.66 0.67 0.70 ZrO₂ + Nb₂O₅ + TiO₂ + WO₃)/ (La₂O₃ + ZrO₂) (ZrO₂ + TiO₂ + La₂O₃)/ 1.39 1.38 1.40 1.39 1.47 1.39 1.35 1.42 1.40 (Nb₂O₅ + SiO₂ + WO₃ + Gd₂O₃) Total amount 100 100 100 100 100 100 100 100 100 Refractive index (nd) 1.876 1.888 1.881 1.883 1.879 1.884 1.887 1.886 1.885 Abbe number (vd) 38.9 39.8 38.9 39.5 39.4 38.8 39.7 39.6 39.4 Upper limit of 1340 1270 1275 1280 1285 1275 1280 1275 1275 devitrification temperature (° C.) Durability of 2 1 1 1 3 1 1 1 1 water (grade) Durability of 3 1 1 1 3 1 1 1 1 acid (grade) Bubble (grade) A₀ A₀₀ A₀₀ A₀₀ A₀ A₀₀ A₀₀ A₀₀ A₀₀ Striae (grade) B A A A B A A A A Climatic resistance 2 1 1 1 3 1 1 1 1 (grade) Density (g/cm³) 5.465 5.467 5.464 5.465 5.560 5.465 5.470 5.460 5.464 λ₇₀(nm) 381 382 381 381 415 381 385 380 381 λ₅(nm) 342 343 342 342 358 342 345 340 342

TABLE 2 Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Component (wt %) ment 10 ment 11 ment 12 ment 13 ment 14 ment 15 ment 16 ment 17 ment 18 B₂O₃ 25.0 11.0 10.0 11.0 11.8 13.4 13.0 12.4 11.1 La₂O₃ 42.0 37.0 35.0 33.0 33.1 45.0 34.1 35.0 35.4 Y₂O₃ 1.0 4.0 4.9 4.3 4.3 0.0 3.4 4.9 2.0 Gd₂O₃ 23.0 21.0 23.0 23.0 22.9 10.0 23.0 22.9 23.0 SiO₂ 2.0 7.9 7.0 6.9 6.0 15.0 6.3 5.6 5.0 ZrO₂ 1.0 4.0 6.0 7.0 6.5 3.0 4.2 5.0 6.5 TiO₂ 1.0 1.9 3.0 2.2 2.5 0.1 3.0 3.0 3.0 WO₃ 4.0 2.0 1.1 1.0 1.0 5.0 1.0 2.5 4.0 Ta₂O₅ 0.0 8.2 8.0 8.7 8.9 5.5 10.0 7.2 7.0 ZnO 0.0 3.0 2.0 2.9 3.0 1.0 2.0 1.5 3.0 Nb₂O₅ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Sb₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SnO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CeO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Yb₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lu₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Al₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Bi₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 GeO₂ 1.0 0.0 0.0 0.0 0.0 2.0 0.0 0.0 0.0 Li₂O + Na₂O + K₂O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CaO + SrO + BaO + MgO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 (B₂O₃ + SiO₂ + 0.77 0.65 0.66 0.70 0.70 0.76 0.72 0.71 0.71 ZrO₂ + Nb₂O₅ + TiO₂ + WO₃)/ (La₂O₃ + ZrO₂) (ZrO₂ + TiO₂ + La₂O₃)/ 1.52 1.39 1.41 1.37 1.41 1.60 1.36 1.39 1.40 (Nb₂O₅ + SiO₂ + WO₃ + Gd₂O₃) Total amount 100 100 100 100 100 100 100 100 100 Refractive index (nd) 1.884 1.885 1.886 1.883 1.882 1.879 1.889 1.888 1.885 Abbe number (vd) 39.2 39.5 39.5 39.9 39.8 39.6 39.5 39.5 39.1 Upper limit 1290 1275 1275 1285 1285 1320 1275 1280 1280 of devitrification temperature (° C.) Durability of 2 1 1 1 1 2 1 1 1 water (grade) Durability of 2 1 1 1 1 2 1 1 1 acid (grade) Bubble (grade) A₀ A₀₀ A₀₀ A₀₀ A₀₀ A₀ A₀₀ A₀₀ A₀₀ Striae (grade) B A A A A B A A A Climatic resistance 2 1 1 1 1 2 1 1 1 (grade) Density (g/cm³) 5.520 5.465 5.462 5.468 5.462 5.600 5.469 5.465 5.464 λ₇₀(nm) 412 381 380 383 380 400 384 381 381 λ₅(nm) 355 342 341 343 341 351 344 342 342

TABLE 3 Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Component (wt %) ment 19 ment 20 ment 21 ment 22 ment 23 ment 24 ment 25 ment 26 ment 27 B2O3 14.0 16.0 13.0 12.0 13.0 12.0 14.0 14.0 10.0 La₂O₃ 37.0 45.0 33.8 35.1 37.0 37.0 37.0 35.8 39.0 Y₂O₃ 2.0 1.0 4.9 2.0 2.4 2.0 2.0 5.0 10.0 Gd₂O₃ 23.0 17.0 23.0 22.8 23.0 23.0 22.5 20.0 17.0 SiO₂ 5.0 15.0 5.8 5.4 5.0 6.0 6.0 5.0 10.0 ZrO₂ 4.0 1.0 4.5 6.8 6.5 5.6 6.5 4.0 7.0 TiO₂ 3.0 1.0 2.5 1.3 1.0 2.0 1.0 1.0 0.0 WO₃ 3.0 0.1 1.0 2.9 4.0 3.5 3.0 4.0 1.0 Ta₂O₅ 7.0 0.0 8.7 9.0 7.1 7.2 7.0 8.2 4.0 ZnO 2.0 3.9 2.8 2.7 1.0 1.7 1.0 3.0 0.0 Nb₂O₅ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.0 Sb₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SnO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CeO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Yb₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lu₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Al₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Bi₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 GeO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Li₂O + Na₂O + K₂O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CaO + SrO + BaO + MgO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 (B₂O₃ + SiO₂ + 0.71 0.72 0.70 0.68 0.68 0.68 0.70 0.70 0.65 ZrO₂ + Nb₂O₅ + TiO₂ + WO₃)/ (La₂O₃ + ZrO₂) (ZrO₂ + TiO₂ + La₂O₃)/ 1.42 1.46 1.37 1.39 1.39 1.37 1.41 1.41 1.53 (Nb₂O₅ + SiO₂ + WO₃ + Gd₂O₃) Total amount 100 100 100 100 100 100 100 100 100 Refractive index (nd) 1.884 1.883 1.886 1.882 1.883 1.889 1.881 1.881 1.887 Abbe number (vd) 39.2 40.8 39.6 39.5 39.4 39.4 39.7 39.5 39.9 Upper limit 1285 1275 1285 1275 1280 1280 1280 1280 1275 of devitrification temperature (° C.) Durability of 1 2 1 1 1 1 1 1 2 water (grade) Durability of 1 2 1 1 1 1 1 1 2 acid (grade) Bubble (grade) A₀₀ A₀ A₀₀ A₀₀ A₀₀ A₀₀ A₀₀ A₀₀ A₀ Striae (grade) A B A A A A A A B Climatic resistance 1 2 1 1 1 1 1 1 2 (grade) Density (g/cm³) 5.460 5.510 5.468 5.465 5.465 5.468 5.462 5.462 5.520 λ₇₀(nm) 380 415 383 381 381 383 380 380 412 λ₅(nm) 340 358 343 342 342 343 341 341 355

TABLE 4 Compar- Compar- ative ative Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- Embodi- exam- exam- Component (wt %) ment 28 ment 29 ment 30 ment 31 ment 32 ment 33 ment 34 ple 1 ple 2 B₂O₃ 10.5 15.0 16.0 10.0 20.0 8.0 18.0 15.0 5.0 La₂O₃ 42.0 39.0 33.0 30.0 45.0 45.0 35.0 45.0 40.0 Y₂O₃ 1.0 0.0 5.0 0.0 0.0 0.0 8.0 8.0 5.0 Gd₂O₃ 25.0 17.0 28.0 25.0 20.0 25.0 29.0 15.0 8.0 SiO₂ 4.0 10.0 0.5 10.0 3.0 15.0 0.5 10.0 5.0 ZrO₂ 10.0 3.0 1.0 15.0 1.0 1.0 7.0 0.0 5.0 TiO₂ 0.5 0.0 5.0 0.0 0.1 5.0 0.0 0.0 0.0 WO₃ 7.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 10.0 Ta₂O₅ 0.0 14.3 1.4 0.0 0.0 0.0 2.5 0.0 2.0 ZnO 0.0 1.7 10.0 10.0 2.4 1.0 0.0 7.0 20.0 Nb₂O₅ 0.0 0.0 0.0 0.0 8.5 0.0 0.0 0.0 0.0 Sb₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SnO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CeO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Yb₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Lu₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Al₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Bi₂O₃ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 GeO₂ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Li₂O + Na₂O + K₂O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CaO + SrO + BaO + MgO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 (B₂O₃ + SiO₂ + 0.62 0.67 0.66 0.78 0.71 0.63 0.61 0.56 0.56 ZrO₂ + Nb₂O₅ + TiO₂ + WO₃)/ (La₂O₃ + ZrO₂) (ZrO₂ + TiO₂ + La₂O₃)/ 1.46 1.56 1.36 1.29 1.46 1.28 1.42 1.80 1.96 (Nb₂O₅ + SiO₂ + WO₃ + Gd₂O₃) Total amount 100 100 100 100 100 100 100 100 100 Refractive index (nd) 1.882 1.887 1.881 1.874 1.881 1.885 1.886 1.858 1.858 Abbe number (vd) 38.7 40.8 39.4 41.0 38.6 39.5 40.7 38.6 38.1 Upper limit of 1280 1275 1270 1285 1280 1295 1300 1352 1352 devitrification temperature (° C.) Durability of 2 2 1 2 2 2 2 4 4 water (grade) Durability of 2 2 1 2 2 2 2 4 4 acid (grade) Bubble (grade) A₀ A₀ A₀₀ A A₀ A₀ A₀ B B Striae (grade) B B A B B B B D D Climatic resistance 2 2 1 2 2 2 2 4 4 (grade) Density (g/cm³) 5.560 5.520 5.469 5.580 5.560 5.580 5.460 5.700 5.800 λ₇₀(nm) 415 410 384 387 415 387 380 440 442 λ₅(nm) 358 352 344 359 358 359 340 370 372

TABLE 5 Comparative Comparative Comparative Component (wt %) example 3 example 4 example 5 B₂O₃ 5.0 8.0 5.0 La₂O₃ 34.0 35.0 40.0 Y₂O₃ 10.0 0.0 0.0 Gd₂O₃ 40.0 35.0 30.0 SiO₂ 0.0 8.0 2.0 ZrO₂ 1.0 5.0 2.0 TiO₂ 0.0 2.0 0.0 WO₃ 10.0 0.0 13.0 Ta₂O₅ 0.0 0.0 2.0 ZnO 0.0 7.0 6.0 Nb₂O₅ 0.0 0.0 0.0 Sb₂O₃ 0.0 0.0 0.0 SnO₂ 0.0 0.0 0.0 CeO₂ 0.0 0.0 0.0 Yb₂O₃ 0.0 0.0 0.0 Lu₂O₃ 0.0 0.0 0.0 Al₂O₃ 0.0 0.0 0.0 Bi₂O₃ 0.0 0.0 0.0 GeO₂ 0.0 0.0 0.0 Li₂O + Na₂O + K₂O 0.0 0.0 0.0 CaO + SrO + BaO + MgO 0.0 0.0 0.0 (B₂O₃ + SiO₂ + ZrO₂ + 0.46 0.58 0.52 Nb₂O₅ + TiO₂ + WO₃)/(La₂O₃ + ZrO₂) (ZrO₂ + TiO₂ + La₂O₃)/ 0.70 0.98 0.93 (Nb₂O₅ + SiO₂ + WO₃ + Gd₂O₃) Total amount 100 100 100 Refractive index (nd) 1.850 1.860 1.852 Abbe number (vd) 38.2 38.5 38.0 Upper limit of devitrification 1358 1350 1355 temperature (° C.) Durability of water (grade) 4 4 4 Durability of acid (grade) 4 4 4 Bubble (grade) B B B Striae (grade) D D D Climatic resistance (grade) 4 4 4 Density (g/cm³) 5.680 5.610 5.650 λ₇₀(nm) 431 430 435 λ₅(nm) 362 365 368 Note: The total amounts (100%) in the tables are data obtained by deducting measurement errors, equipment accuracy and unavoidable impurities.

In the Description, the reference terms “one embodiment”, “some embodiments”, “example”, “specific example”, or “some examples”, etc. are described to refer to that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the Description, the illustrative expressions of the terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be appropriately combined in any one or more embodiments or examples. In addition, without any contradiction, those skilled in the art can integrate or combine different embodiments or examples or features of different embodiments or examples described in the Description.

Although the embodiments of the present disclosure have been illustrated and described, it can be understood that the embodiments are exemplary and should not be construed as limitations thereto. Changes, modifications, replacements and variations within the scope of the present disclosure can be made to the embodiments by any ordinary person skilled in the art. 

The invention claimed is:
 1. An optical glass, comprising: 5 to 25 wt % of B₂O_(3;) 25 to 45 wt % of La₂O_(3;) 0 to 10 wt % of Y₂O_(3;) 10 to 35 wt % of Gd₂O_(3;) 0.5 to 15 wt % of SiO_(2;) 1 to 15 wt % of ZrO_(2;) 0 to 5 wt % of TiO_(2;) 0 to 7 wt % of WO_(3;) 0 to 15 wt % of Ta₂O_(5;) 0 to 10 wt % of ZnO; and 0 to 8.5 wt % of Nb₂O_(5,) wherein m_((B) ₂ _(O) ₃ _(+SiO) ₂ _(+ZrO) ₂ _(+Nb) ₂ _(O) ₅ _(+TiO) ₂ _(+WO) ₃ ₎/m_((La) ₂ _(O) ₃ _(+ZrO) ₂ ₎ is not lower than 0.6 and not more than 0.7, and m_((ZrO) ₂ _(+TiO) ₂ _(+La) ₂ _(O) ₃ ₎/m_((Nb) ₂ _(O) ₅ _(+SiO) ₂ _(+WO) ₃ _(+Gd) ₂ _(O) ₃ ₎ranges from 1.35 to 1.6.
 2. The optical glass according to claim 1, further comprising: 8 to 20 wt % of B₂O₃; and/or 30 to 42 wt % of La₂O₃; and/or 0 to 8 wt % of Y₂O₃; and/or 15 to 28 wt % of Gd₂O₃; and/or 2 to 13 wt % of SiO₂; and/or 1 to 10 wt % of ZrO₂; and/or 0.1 to 5 wt % of TiO₂; and/or 0.1 to 5 wt % of WO₃; and/or 0.5 to 10 wt % of Ta₂O₅; and/or 0 to 5 wt % of ZnO; and/or 0 to 8.5 wt % of Nb₂O_(5.)
 3. The optical glass according to claim 1, further comprising: 10 to 16 wt % of B₂O₃; and/or 33 to 39 wt % of La₂O₃; and/or 1 to 5 wt % of Y₂O₃; and/or 17 to 25 wt % of Gd₂O₃; and/or 4 to 10 wt % of SiO₂; and/or 3 to 8 wt % of ZrO₂; and/or 0.5 to 3 wt % of TiO₂; and/or 0.5 to 4 wt % of WO₃; and/or 3 to 10 wt % of Ta₂O₅; and/or 1 to 3 wt % of ZnO; and/or 0 to 8.5 wt % of Nb₂O_(5.)
 4. The optical glass according to claim 1, further comprising: 0 to 1 wt % of Sb₂O₃; and/or 0 to 1 wt % of SnO₂; and/or 0 to 1 wt % of CeO₂; and/or 0 to 10 wt % of YbO₃, and/or 0 to 10 wt % of Lu₂O₃; and/or 0 to 10 wt % of Al2O₃; and/or 0 to 10 wt % of Bi₂O₃; and/or 0 to 10 wt % of GeO₂; and/or 0 to 10 wt % of total amount of Li₂O, Na₂O and K₂O; and/or 0 to 10 wt % of total amount of CaO, SrO, BaO and MgO.
 5. The optical glass according to claim 1, wherein m_((B) ₂ _(O) ₃ _(+SiO) ₂ _(+ZrO) ₂ _(+Nb) ₂ _(O) ₅ _(+TiO) ₂ _(+WO) ₃ ₎/m_((La) ₂ _(O) ₃ _(+ZrO) ₂ ₎ ranges from 0.65 to 0.7.
 6. The optical glass according to claim 1, wherein m_((ZrO) ₂ _(+TiO) ₂ _(+La) ₂ _(O) ₃ ₎/m_((Nb) ₂ _(O) ₅ _(+SiO) ₂ _(+WO) ₃ _(Gd) ₂ _(O) ₃ ₎ is equal to 1.35-1.45.
 7. The optical glass according to claim 1, wherein m_((ZrO) ₂ _(+TiO) ₂ _(+La) ₂ _(O) ₃ ₎/m_((Nb) ₂ _(O) ₅ _(+SiO) ₂ _(+WO) ₃ _(+Gd) ₂ _(O) ₃ ₎ is equal to 1.35-1.42.
 8. The optical glass according to claim 1, having a refractive index of 1.87 to 1.89, an abbe number of 39.0-41.0, a λ₇₀ of not more than 390 nm, a λ₅ of not more than 350 nm, a devitrification temperature having an upper limit of not higher than 1300° C., a durability of water of not lower than grade 2, a durability of acid of not lower than grade 2, a climatic resistance is not lower than grade 2, a striae of above grade A, an extent of bubble of not lower than grade A₀₀, and a density of not higher than 5.5 g/cm^(3.)
 9. The optical glass according to claim 1, wherein a refractive index of the optical glass is more than 1.86, and abbe number thereof is more than 38.8.
 10. The optical glass according to claim 1, wherein λ₇₀ of the optical glass is not more than 420 nm, and λ₅ thereof is not more than 360 nm.
 11. The optical glass according to claim 1, wherein an upper limit of devitrification temperature of the optical glass is not higher than 1350° C.
 12. The optical glass according to claim 1, wherein have a durability of water of not lower than grade 3, a durability of acid of not lower than grade 3, and a climatic resistance of not lower than grade
 3. 13. The optical glass according to claim 1, wherein striae of the optical glass is above grade C.
 14. The optical glass according to claim 1, wherein having an extent of bubble of not lower than grade A.
 15. The optical glass according to claim 1, having a density of not higher than 5.6 g/cm³.
 16. A glass preform made of the optical glass according to claim
 1. 17. An optical element made of the glass preform according to claim
 16. 18. An optical element made of the optical glass according to claim
 1. 19. An optical instrument with the optical element according to claim
 18. 